Gut microbe linked to depression in large health study | Science

The trillions of bacteria in and on our bodies can bolster our health and contribute to disease, but we don’t know exactly which microbes are the key players. Now, a study involving thousands of people in Finland has identified a potential microbial culprit in some cases of depression.

The finding, which emerged from a study of how genetics and diet affect the microbiome, “is really strong evidence that this association could have major clinical significance,” says Jack Gilbert, a microbial ecologist at the University of California at San Diego, which was not involved in the work.

Researchers are increasingly discovering links between brain conditions and gut microbes. People with autism and mood disorders, for example, have deficits of certain key bacteria in their gut. Whether these microbial deficits actually contribute to causing the disorders is unclear, but the findings have spawned a rush to exploit gut microbes and the substances they produce as possible treatments for a variety of brain disorders. Indeed, researchers have recently reported in Frontiers in psychiatry that fecal transplants improved symptoms in two depressed patients.

Guillaume Méric did not seek to find microbes that cause depression. A microbial bioinformatician at the Baker Heart & Diabetes Institute, he and his colleagues were analyzing data from a large Finnish health and lifestyle study. As part of a 40-year effort to research the underlying causes of chronic disease among Finns, the 2002 study assessed the genetic makeup of 6,000 participants, identified their gut microbes and compiled detailed data on their diet. diet, lifestyle, prescription drug use and health. The researchers tracked the participants’ health through 2018.

Méric and his colleagues combed through the data to find clues about how a person’s diet and genetics affect the microbiome. “There have been very few studies that have examined [all these factors] with so much detail,” says Gilbert. Two sections of the human genome appear to have a strong influence on the microbes in the gut, researchers report this week in Natural genetics. One contains the gene for digesting milk sugar, lactose, and the other helps specify blood type. (A second study, also published today in Natural geneticsidentified the same genetic loci by analyzing the relationship between the genomes and gut microbes of 7700 people in the Netherlands.)

Méric’s team also explored which genetic variants might affect the abundance of certain microbes and which of these variants were linked to 46 common diseases. When it comes to depression, two bacteria that cause infections in hospitalized patients, Morganelle and Kiebdiella, seems to play a causal role, say the researchers. One of them, Morganellewas significantly increased in a microbial survey of the 181 people in the study who later developed depression.

“It’s really exciting,” says Jeroen Raes, a microbiologist at KU Leuven who was not involved in the study. “The beauty of the work,” he adds, is that Méric and his colleagues have linked increased levels of the bacteria to patients suffering from depression.

Morganelle has previously been implicated in depression. As early as 2008, researchers investigating a possible link between depression and inflammation found that depressed people had stronger immune responses to chemicals produced by Morganelle and other gram-negative bacteria in the gut. So the latest study appears to be “further evidence” that inflammation caused by gut microbes can influence mood, Gilbert says.

But the field is still in its infancy, says Gerard Clarke, a microbiome researcher at University College Cork, because there are many forms of depression and many possible ways in which microbes could affect this disease. The “holy grail” is to identify a missing microbe that could be supplemented, he says. But it’s less clear how Morganelle could be eliminated from the intestine to relieve symptoms. “It’s a little more difficult.”

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